The electrochemical polymerization of 5-membered and 6-membered heterocyclic compounds, particularly of pyrrole, is laid open in the specification of U.S. Pat. No. 3,574,072.
That the anodic oxidative polymerization of pyrrole in the presence of a conductive salt results in forming film with the conductivity of less than 10.sup.2 S cm.sup.-1 on the anode is described in A. F. Diaz, et. al: J.C.S. Chemical Communication (J.C.S. Chem. Comm. P635 (1979)).
It is defined in this technical field that polymer film containing the anion of the conductive salt and formed on the anode is said to be doped in the P type (oxidation state) and the state of which the anion, a dopant, is taken out from the inside of the molecule is said a undoping state (reduction state). The polymer film is known to have high conductivity in the doping state and extremely low conductivity in the undoping state, and to display the electrochromism when changing between the two states.
The polymers of 3,4-substituted pyrrole, especially of 3,4-asymmetrically substituted pyrrole compounds have general descriptions but few of them have been synthesized. No documents describing particularly polymers of pyrrole compounds having an electron attractive substituent at C.sub.3 or C.sub.4 have not been yet known.
The aforementioned polymer film of pyrrole compounds display the electrochromism, and have however no clear beautiful color changes. When letting stand alone in the air in the undoping state, the film is oxidized to change the color to black and thus does not exist stable in the undoping state. The polymers are usually insoluble and not melting.
Therefore, industrially useful materials or electronic devices employing the film have not been obtained yet.